texts: What would happen if a star passed through the barycenter of two binary stars?

texts: I was doing some research on Alpha Centauri A and B, and thought to myself: 'What would happen if something passed directly through the barycenter of these two stars?' I may theorise that a passing star will offset the barycenter with its gravity, sending the two stars in whatever direction it would go. I am not certain about this, nor am I certain that anyone has the answer. But if they do, please answer, I'd really like to know!


texts: Tips for a beginer who wants to learn more about astronomy

texts:
I have completely no idea about astronomy, but I am starting growing interest in it as I have been always wondering on what has been discovered out there and since I am studying CS, maybe I will learn more than I think as CS and astronomy as relative to some point. How should I start? Can you suggest me a good website for example or something else?

(I know this is an opinion - based question but still I need to make this question here).


texts: Do meteors always streak in the same direction? While I know it's not likely to be exactly the same direction, but generally speaking. Would one say meteors always travel, for example, east to west?


texts: How to calculate magnitude of a star in a triple star system?

texts: I want to find a star's magnitude in a triple star. I already knew the the magnitude of the triple star and the other two star, but I don't quit know how to solve it. Is there a way to find it?


texts: What does "Normalized to Si 10 to the power 6" mean?

texts: I'm writing a space game that I want to give a more "realistic" feel. When looking for a reference as to distribute elements in planets (for mining, etc) Instead of finding the more usual percentage tables, it seems that all elements are presented in a "normalized to Si 10 to the power 6", and furthermore, it seems that the data is presented as number of atoms, instead of actual mass. I've been searching this for days, and even the "parts per million/billion/trillion" tables sometimes just jump for percentages, where is is again no clear if what is being referred to are masses or number of atoms. Could someone clarify this, or better, point me to a mass percentage table of elements in a solar system/galaxy for reference? Thanks in advance.


texts: Are all planets/galaxies moving away from *us*?

texts:
From what I can see in a physics textbook page (on redshift), it seems to imply that all planets/galaxies emit red, rather than blue waves (for red-shift).

Wouldn't this mean that everything is moving away from us and that we're the centre of the Big Bang? (See quote from the book below)

On a similar note, does everything move at the same speed away from the centre of the Universe? - If not, then wouldn't that mean that we'd see a few planets/galaxies that emit blue, as they are traveling with a greater velocity from the centre than we are (with it being closer to the centre) and that they are 'catching up' with us?

It's not a big deal and I don't need to know it, but I would like to know, if possible.

~StratusGold

Quoting the textbook: "When we look at light from distant galaxies, we find that the wavelength has increased. The wavelengths are longer than they should be - they're shifted towards the red end of the spectrum. This is called red-shift. (...omitted...) Measurements of the red-shift indicate that these galaxies are moving away from us (receding) very quickly - and it's the same result whichever direction you look in" - CGP GCSE AQA 9-1 Physics Revision Guide, Topic 8 'Space Physics', Pg 102


texts: How do you fit a model SED to an observed galaxy spectrum with photometric data?

texts:
I have a spectrum of a galaxy from HST data and SDSS data (resulting in a nearly continuous SED from the FUV~1000 Angstroms through infrared). I have created a model SED with the galaxy simulation software STARBURST99 (for the correct star formation, age and type of evolution for the real galaxy) to extend from ~90 Angstroms through the infrared. I then reddened my model spectrum with the Cardelli et al. (1989) extinction law. I also have various photometric multi-band data from different surveys. I understand that I need to use this data to adjust my model spectrum so that it is a good fit of the observational SED and matches observations at each photometric point. But I'm confused on how I would go about this normalization/calibration process of my model spectrum.

Is it as simple as linear offsets in flux at these various different points? I doubt that, however, because that would then seem difficult to keep my model spectrum smooth. I'm unsure if I really understand the process of proper SED fitting in the first place... Any help with this concept and how I could use photometric multi-band data to increase the goodness of fit of my model is greatly appreciated!


texts: Where can I look up the 3D positions of the closest stars?

texts:
The problem:

I want to simulate a travel from Earth to the closest 15-25 stars. Which is the fastest way to accomplish this?

What i have:

I currently have the distance between Earth and the nearby stars, according to this link: http://www.space.com/18964-the-nearest-stars-to-earth-infographic.html. But from it I can't know if Alpha Centauri (4.3 light-years from Earth) is closest to Sirius (8.58 light-years from Earth) or to Wolf 359 (7.8 light-years from Earth).

What I need:

I need the distance between any two stars, at least the closest ones to Earth. Then it would be possible to run a Traveling Salesman problem, in order to visit all the nearby stars (or a subset of 15-25 of them) in the fastest time.

Where can I get this information?


texts:
I know Hubble's galaxy classification scheme and the bifurcation from elliptical galaxies into two types of spiral ones. I am also aware of different theories on how spiral galaxies form e.g. through collision with another one. I was always wondering in how much any kind of galaxy morphological classification actually relates with the dynamics of a galaxy. The following paragraph of the Wikipedia article seem to support my uncomfort:

To this day, the Hubble sequence is the most commonly used system for classifying galaxies, both in professional astronomical research and in amateur astronomy. Nonetheless, in June 2019, citizen scientists through Galaxy Zoo reported that the usual Hubble classification, particularly concerning spiral galaxies, may not be supported, and may need updating.

Differently put: Would a lone elliptical galaxy eventually become a spiral one? And if so, how to define the transition point? For me, it does not appear obvious how to set a threshold after which density fluctuations within an elliptical galaxy deserve to be called spiral arms. More technical: Which confidence band around the average radial density distribution of a given galaxy has to be breached in order for the galaxy to be called spiral?
Related

Evolution of galaxies with time
How small can a spiral galaxy be?
How do disk-shaped galaxies then form at the sites of spherical galactic halos? Do the halo stars start orbiting or just sit in place?


texts: How to calculate the pixel size and beam size of an image?

texts: I have an image with some sources in it. I need to get the pixel size and beam size of that image. How can I calculate it?


texts: Some of the ultra-hot Jupiters (WASP-33b, KELT-9b) have dayside surface temperatures similar to low-mass stars. Would they be capable of producing flares? To be specific, I am asking about the possibility of flaring on the planet itself, rather than the planet inducing flares on the star.


texts: Safety while using a telescope to view a total solar eclipse

texts: I have an 8-inch reflector telescope and a solar filter that goes on the front aperture to view the Sun (most recently to view the transit of Mercury). If I were to use this telescope during a total solar eclipse, would it be safe to remove the filter during totality? Let's assume I also get the filter back on before totality ends.


texts: Do solar systems have to evolve in a galaxy?

texts: Is it possible for a solar system like ours to exist and evolve apart from all other star systems and galaxies. Sort of like a stand alone solar system or rogue solar system for lack of a better name. Or is there some requirement that a solar system capable of managing and growing planets especially ones that will occur in the habitable zone originate in a galaxy?


texts: How do I get focussed images with my T-adaptor and 6mm eyepeice?

texts:
I have a Celestron 5se + canon 650d. They are mated with the celestron t-ring and the 93625 t-adaptor.
I want to take magnified photos of planets with the camera. But if I add an eyepiece to the t-adaptor, everything gets blur.
Here are some scenarios that highlight the problem:

look at Jupiter with 25mm eyepiece in telescope: clear and focused image
look at Jupiter with 6mm eyepiece in telescope: clear and focused zoomed image
look at Jupiter with camera and no eyepiece inside the t-adaptor, in telescope: clear and focused image but small.
look at Jupiter with camera and 6mm eyepiece inside the t-adaptor, in telescope: large unfocused ball

I dont know how to solve this.
Clearly, the 93625 t-adaptor was made to accept an eyepiece and lock it with the thumbscrew, but why does it not result in focused images?


texts: How is the height of the Great Red Spot measured?

texts: This answer states that the Great Red Spot is getting taller. This means that we are able the determine the spot's height. How do we do this?


texts:
I was lying down with my face up looking at the stars. Then I saw this star moving:

it was moving at one direction (just like airplane)
it's light was not blinking, just exactly as other stars both In color, brightness, size
it took around 90 seconds before it disappeared from my view.

This happened in eastern Nigeria

What could it be? If it's a star what kind of star is that?


texts: Wavelength Calibration in Python - Line Identification algorithm

texts:
I was asked to develop a data reduction pipeline for a telescope and am facing a problem.

I have the standard lamp spectra and need to identify the emission lines in order to find a wavelength solution to apply to the spectra taken.

I managed to find the signal peaks and calculate their centroids, I am unsure - however - of how to match the centroids I found with a list of the emission lines of the lamps.

I basically have to do what "Identify" in IRAF does, but in python. I know there have been some packages that do that (like specutils), but they are outdated and recall deprecated libraries.

Any tip on where to go or what to do to have a centroid-wavelength match would be greatly appreciated.


texts: Reshaping black holes to "push" the event horizon

texts:
I watched this simulation made by LIGO (Laser Interferometer Gravitational-Wave Observatory) where 2 black holes merge into one.

https://www.youtube.com/watch?v=I_88S8DWbcU

I was therefore thinking that theoretically nothing can escape a black hole given the features of the space and the black hole remain the same due to the strong gravity.

However, I was thinking if 2 black holes stay together close enough, the "event horizon" would reshape as well.

We all know the gravity force is F=G(Mm/r^2).

Given a point next to the event horizon but "inside" the black hole the gravity there will be so strong that the Escape velocity will be higher than C (speed of light).

If we place another massive object (like another blackhole in the proximities of this point, but far enough, the gravity there will be counteracted and therefore this point will be able to escape its black hole, reshaping the event horizon and making it smaller. (We will have created a "concavity" in the event horizon)

My question is:

Given a hypothetical scenario where we create thousands of micro blacholes orbiting the main blackhole, in a gravitational equlibrium. Would we be able to reshape and "push" the event horizon strong enough that objects inside could now use the chance and escape?

Could we even pull the matter of the black hole and make it less dense along the time even transforming it into a start destroying the singularity?


texts: Why does the precession of the earth affect other planets?

texts:
In the Wikipedia article on numerical integration of planetary motion it states:

  ...the flattening of the Earth causes precession, which causes the
  axial tilt to change, which affects the long-term movements of all
  planets.

Why would precession affect the motion of the other planets?


texts: Why the more-luminous star has larger surface area when two stars have the same temperature?

texts:
If two stars have the same temperature but one is more luminous than
  the other, the more-luminous star must have a larger surface area, and
  therefore a larger radius than the dimmer star.

The light density of the two stars is obviously different. Must the brighter star have more lights?


texts: Demonstration of scales for the two components (transverse and perpendicular) of Baryonic Acoustic Oscillations (BAO)

texts:
I transfer here a post that has not had any answer pn physics exchange, so I am going to delete this latter. Maybe I will have more luckiness here.
In an astrophysics context about BAO (Baryonic Acoustic Oscillation), it is written on the following paper BAO paper :
"BAO are much smaller in amplitude than the CMB acoustic peaks, and are washed out on small scales. BAO in the observed galaxy power spectrum have the characteristic scale determined by the comoving sound horizon at recombination, which is precisely measured by the CMB anisotropy data $[12] .$ In principle, the BAO scale can be extracted from data both in the transverse direction $\left(s_{\perp}\right),$ and along the line-of-sight $\left(s_{\|}\right)$, i.e radial. Comparing the observed BAO scales with the expected values gives the angular diameter distance $D_{A}(z)=r(z) /(1+z)(\text { where } r(z)$ is the comoving distance $)$ in the transverse direction, and the Hubble parameter $H(z)$ in the radial direction:
\begin{aligned}
s_{\perp} & \propto \frac{s}{D_{A}(z)}\quad(1) \\
s_{\|} & \propto s H(z)\quad(2)
\end{aligned}
]
Seo & Eisenstein (2007) (11] (henceforth SE07) provided simple fitting formulae for forecasting the accuracies of $s / D_{A}(z)$ and $s H(z)$ from future galaxy redshift surveys. In this paper, we will clarify the assumptions made in BAO forecasts, and investigate their implications. We will discuss the method in Sec.2, present results on BAO forecasts in Sec.3, and summarize in Sec.4."
Concerning my question, I don't understand the justification/origin of the 2 equations in $(1)$.
i.e :
$$
\begin{aligned}
s_{\perp} & \propto \frac{s}{D_{A}(z)}\quad(1) \\
s_{\|} & \propto s H(z)\quad(2)
\end{aligned}
$$
Indeed, assuming we have just a pure transverse component $s_{\perp}$ :
then, the angular under which it is observed is :
$\theta \simeq \tan(\theta) = \dfrac{s_{\perp}}{D_{A}(z)}\quad(3)$
with $D_{A}(z)$ the angular diameter distance, i.e the physical distance of "objects" at given redshift ( I think from the paper that it is equal $D_{A}(z)=r(z) /(1+z)(\text { where } r(z)$ is the comoving distance).
By the way, with this notation, $r(z)$ comoving distance is actually the cosmological horizon, i.e $r(z=1100) \approx 44\,\text{Gyr}$, isn't it ?
But back to equations $(1)$ and $(2)$.
So for a pure transverse component, I have a first element of answer for $(1)$ but not totally since I don't know how to make the link between $\theta$ and $s$ BAO scale.
And Moreover, what about the equation $(2)$ :
how to get it ? It makes think to the Hubble-Lemaître law of expansion but $s_{\|}$ is a distance and not a velocity. ok, there is a $\propto$ relation but I would like to  know where this relation comes from.
If someone could help me to proove these 2 relations $(1)$ and $(2)$. Naively, I would have thought that $s_{\|} = s_{\perp}$ if Universe is homogenous but this is not the case actually and I don't understand why ?
UPDATE 1: From this paper BAO scales , I am expecting inverted formulas for $eq(1)$ and $eq(2)$. Indeed, here an image from this given paper illustrating the 2 quantities :

So, compared to what is shown in $eq(1)$ and $eq(2)$, I would rather say that :
$$
\begin{aligned}
d_{A}(z)& =\frac{s_{\perp}}{\Delta\theta}\quad(3) \\
s_{\|} & = \Delta z \frac{c}{H(z)}\quad(4)
\end{aligned}
$$
From $eq(3)$, we could infer for $s_{\perp}$ :
$$s_{\perp} = d_{A}(z)\,\Delta\theta\quad(5)$$
So, as conclusion, how to make the link between (1),(2) definitions and ((4),(5)) : I don't grasp very well the parameter s :
Can we write that $$s^2=s_{\perp}^2+s_{\|}^2$$ ?
If this is the case, how to conclude to be consistent between the 2 papers ?
Any help is welcome.


texts: What are the sources of antimatter particles in the magnetosphere?

texts:
The PAMELA instrument detected antimatter particles in the Earth's magnetosphere.  What are the sources of these particles?

The answer to Source of high energy cosmic particles outlines the sources of cosmic rays in general, does it still hold true for antimatter particles?


texts: Is there a connection between the solar wind and the cosmic radiation?

texts:
Cosmic radiation consists of high-energetic particles, mostly protons, that come amongst others from supernovae and our sun, right?
The solar wind also consists of charged particles, like protons and electrons, and comes, of course, from the sun.
So I wonder whether there is a connection between these two? Is the solar wind a part of the cosmic radiation?


texts: How likely does a body more massive than Eris exist beyond the Kuiper belt?

texts: Other than the hypothetical Planet IX, is it likely if there's a (dwarf) planet more massive than Eris orbiting between Eris and Planet IX? Michael Brown seems to have found it likely. As far as we know about the many Kuiper-belt-and-beyond objects now, can we exclude a more massive body beyond Eris or is it possible that there's such massive body at, let's say, 150 au from the Sun?


texts: I need to study space, planets and black holes, how do I study them on my own, knowing that I am an Arab and I do not know English. I use translation applications. I speak with you. Can you help me with a site or YouTube channel? I don’t want books


texts: Finding the suns position in the sky anywhere at any time

texts:
What am I looking for?

from any point Latitude, Longitude and date D

I want to know where the sun is in the sky at any given time anywhere on our planet. I even don't know what the outcome will be for this calculation. I Imagine an angle and a height.

Can someone send me on the right path for doing this?

I am not looking for a quick formula that let's me calculate this bur rather understand the components :)


texts: Why is Starlink polluting the night sky a big concern if we have space telescopes?

texts:
There's a lot of concern in the Astronomy community over the deployment of Starlink satellites. For a good discussion, see the related question How will Starlink affect observational astronomy?
But why is there so much concern over this problem, given that there are numerous space telescopes? Presumably a lot more will be launched in the upcoming years thanks to satellite launches becoming cheaper. Aren't space-based observations superior in the first place thanks to the lack of an atmosphere?
I understand this sucks for amateur astronomers but is it also a big problem for professional researchers?


texts: Was Guth inflation propelled by what we now call "Dark Energy"?

texts:
The more powerful our telescopes become, the more we are able to see earlier and earlier remnants of Guth Inflation. Assuming that it makes sense to associate a location, BB,  in space-time where the Big Bang occurred, then test particles (luminous or otherwise) have been decelerating away from BB ever since. When viewed through our telescopes, i.e.: when viewed in time reversed order, a test particle decelerating away from BB would appear to be accelerating away from us. We usually attribute this acceleration away from us as propelled by “Dark Energy”, and any study to understand Dark Energy is equivalent to a study of what propelled Guth inflation in the first place.
I am sure that I am not the first to think of such a straight forward interpretation of Dark Energy, but I do not see it in any of the popular literature on Cosmology. This implies that my thinking is probably incorrect. Can somebody point out the flaw?


texts: Ergospheres are a property of black holes, and do neutron stars have it? If yes, why seldom article mentions that; if no, why can't neutron stars have this ergosphere component?


texts: Is threre a relation between relative or absolute error and standard deviation for ratio of power spectra?

texts:
I have to compute the variance on this ratio, that is to say on the observable $O$ :
$$O=\left(\frac{C_{\ell, \mathrm{gal}, \mathrm{sp}}^{\prime}}{C_{\ell, \mathrm{gal}, \mathrm{ph}}^{\prime}}\right)=\left(\frac{b_{s p}}{b_{p h}}\right)^{2}\quad(1)$$
where $C'_{\ell}$ are angular power spectra (or matter power spectra).
Can I apply for this the computation of relative or absolute error like in electricity, we have $U=RI$ and the error on the quantity $R$ :
$$\dfrac{\Delta R}{R}= \dfrac{\Delta U}{U}+\dfrac{\Delta I}{I}$$
Is there a relation between absolute or relative error with the standard deviation of theses ratio ?
I would like to apply it to equation($1$) to compute this error or variance : is the right method ?
If not, which solution would be possible ?
I have difficulties to grasp the subtilities between uncertainty and standard deviation : I just need to compute $\sigma_{o}^{2}$.


texts: How is it ensured that a parabolic shape forms while polishing a telescope mirror?

texts: I understand polishing the mirror with a successively finer abrasive can create a curvature, but how is it possible to obtain a uniform curve that forms a parabola while polishing by hand?


texts: There's a fair amount of info out there about the mass-luminosity relation, i.e. giving some approximate equations for the luminosity of a main sequence star as a function of its mass, e.g. $L_* = M_*^4$ (relative to the Sun's mass and luminosity, for stars close in mass to the Sun). But main sequence stars grow brighter as they age. Are there any resources that give some approximate equations for a star's luminosity (and other parameters like diameter and temperature) as a function of both mass and age?


texts: When we see half moon, why is it always the lower half?

texts:
Even if we see a crescent moon, always the lower circumference is visible. Why we never see this?

PS: this image is vertically inverted.


texts: Is expanding universe adding potential energy?

texts: A system with two massive bodies has potential energy proportional to their separation. Since the universe is expanding, is the potential (and total?) energy of such a system slowly increasing? What is the scale of this effect if it exists?


texts: Expanded element (and molecule) abundance graph?

texts:
There is the "classical" nucleosynthesis timeline chart where the $\log ({\rm mass \,fraction})$ is plotted as a function of $\log(t)$ where $t$ is in seconds after the big bang, looking e.g. as follows

Source
I am searching for the same chart reaching out a bit further towards 17 on the $x$-axis (which would be right now) and I am wondering whether such a thing exists (and what would be the appropriate search terms for a knowledge database).
References

Can you recommend a book about big bang nucleosynthesis and chemical abundances?
XKCD Timeline of the universe explained


texts: Is there a gas giant orbiting TRAPPIST-1?

texts: I would like to know if besides these planets, astronomers have discovered a gas planet like Jupiter in this system and if on these planets could exist life without a comet protector like Jupiter does for the Earth.


texts: Is a swimming pool analogy to building of black holes in the centers of galaxies valid?

texts:
In our garden, we have a little pool to enjoy our 2 children. It is 3 meters in diameter and contains some 4 m³ of water.

For cleaning-convenience every evening I go walking some 5 or 10 rounds in the pool all in the same direction, to set up a relatively fast rotating current in the pool. As a result, all of the remaining dirt (leaves, insects and seeds) are gathered together in the middle of the pool, where they can be easily removed.

So the analogy to galaxies is as follows:

The pool represents the galaxy.
The water represents the space-time? (or all we cannot see in a galaxy? Or the galaxy as a whole?)
The dirt represents barionic matter which is forced to be dense in
the center of the galaxy, hence building the super massive black
hole.

It is clear that it is perhaps no good idea trying to map a 3m standup pool to a 100000 lightyear galaxy, but the observation seems to be worth a thought (and I do not think that I am the first one searching for analogies in that direction).

The question now is, could this be a valid analogy to the process of building supermassive black holes as a result of rotation?


texts: How to convert .mt file with a spectrum to a more convenient format, please? I am able to display that in fv: Fits Viewer, but I am lost in converting. Thank you


texts: Figure out the location of celestial objects relative to the Milky Way in x, y, z co-ordinates

texts:
I am trying to place various celestial objects the correct distance from the Milky Way, using x, y, z co-ordinates.
So assuming the centre-of-mass of the Milky Way is at 0, 0, 0 - how can I figure out where to place a galaxy or star given it's celestial coordinates?
I'm just an amateur, and pushing 60 years old, so please excuse me if I have something wrong here...


texts: Why Free-Free emission is regarded as Thermal emission?

texts: I read that thermal emission/radiation are the ones whose spectra is similar to that of a Black body radiation. Also thermal radiation depends solely on the temperature of the object. How can we consider Free-Free emission and spectral line emission as thermal emission processes? kindly explain


texts: How Does Black Hole Evaporation Look From the Inside?

texts:
Imagine you're inside a black hole event horizon. The curvature of spacetime is such that the direction towards the singularity becomes timelike, as reverse movement becomes literally impossible.

How would Hawking radiative evaporation look like from inside the black hole? From the outside perspective, we know that black holes form (from our time dimension perspective) and then evaporate at a rate that is an inverse function of their mass.

Hawking radiation is created when the vacuum state at the horizon looks as if it is transformed into a non-vacuum state for a distant observer, resulting in a negative energy 'input' to the black hole. If the energy loss this way is not compensated by inputs from outside, the black hole event horizon should gradually shrink, resulting in eventual evaporation. How if at all would that be perceptible by an observer inside the black hole horizon?

Similar question, but no accepted answer.


texts: Do interstellar rocks pose a threat to interstellar travel?

texts:
In the recently released movie Passengers the ship hits a chunk of rock about the size of a softball that punches through multiple layers of hull and creates a problem.

Assuming that a spaceship is traveling away from Earth at near light speed through interstellar space for a distance of 2 to 10 light years is there a significant probability that it would hit a rock that could do serious damage?


texts: How long can the comet C/2020 F3 (NEOWISE) will observed with the naked eye or small optics?

texts:
In the answer to the question
Where should I be looking to see Neowise in southern Sweden?
there is a picture with the comet positions till 30 July. In other sources I saw similar pictures also with 30 July as a last day. Will it be visible a couple days (or a week) after? Or it is totally unclear at now?
I live in a big city with a lot of ground light sources and high buildings and conditions for observations is not always acceptable. I have saw the comet about 19-20 July both with naked eye and with the 20x...50x monocular. And the next favourable period of observations begins about 27 July.
Thanks in advance.


texts: Why Venus evolved so differently from Earth?

texts: I read somewhere that the reason why Venus has a runaway greenhouse effect and Earth doesn't is the former's inability to form separate tectonic plates due to slightly higher temperature softening the then-cooling tectonic plate, preventing its fracture and thus disabling the $\mathrm{CO}_2$ scrubbing function of tectonic activity, which absorbs $\mathrm{CO}_2$ from air by rock weathering and then puts it back into the mantle. And once $\mathrm{CO}_2$ is a runaway in the atmosphere $\text{H}_2\text{O}$ and $\text{SO}_2$ will join forces with it multiplying the greenhouse effect. Therefore, the surface temperature of Venus rose to astonishing values long before life formed on Earth. Is this theory at least possibly correct?


texts: Where might astrometric observations of the Roadster spacecraft be catalogued?

texts:
above: (see small red lines near center of image) Tesla Roadster. 18 Feb. 2018, 11:28 UT. The image above comes from the average of ten, 300-seconds exposures, remotely taken with the 16”-f/3.75 robotic unit (“Pearl”) of Tenagra Observatories in Arizona. The Tesla Roadster is marked with two red lines. At the imaging time, the car was about 3.5 millions of km from the Earth, that is 9 lunar distances. The object was at mag. 21.0. Image by Gianluca Masi (The Virtual Telescope Project) and Michael Schwartz (Tenagra Observatories, Ltd). From Virtual Telescope Project.

below: Zoomed in and cropped showing Roadster's image.

This excellent answer from @MikeG shows exactly how to find a list of observations for a minor planet. But I'd like to ask about a list of observations of an artificial object.

Currently the NASA JPL's Horizons site is also providing predicted trajectory of an unusual spacecraft which is referred to as Roadster. It is the cherry-red Tesla Roadster attached to a roughly 3.6 x 8 meter white rocket body in heliocentric orbit, and it has been tracked by many different observatories because of its unique circumstances. (some GIFs in this answer) Roadster's 4.6 minute rotational period was also recently reported.

Currently Horizons is reporting solution #7. They have been updating their solutions regularly as new observations are made and reported because as Roadster recedes from Earth it is rapidly dimming and will soon pass magnitude +20, so each new solution helps for the reacquisition of the object as it dims.

  This trajectory is based on JPL solution #7, a fit to 269 ground-based optical astrometric measurements spanning 2018 Feb 8.2 to 13.4.

Would these observations still be catalogued in an astronomical database of observations? Since it's not a natural minor planet, it seems the Minor Planet Center would not be hosting this information, but it seems it should still be made available to astronomers for identification purposes.

But where?

The header of the Horizons output includes this:

*******************************************************************************
Revised: Feb 13, 2018          Tesla Roadster (spacecraft)             -143205
          (solution #7)

 Tesla Roadster (AKA: Starman, 2018-017A)

and this:

TRAJECTORY:
  This trajectory is based on JPL solution #7, a fit to 269 ground-based
  optical astrometric measurements spanning 2018 Feb 8.2 to 13.4.

  Trajectory name                       Start (TDB)          Stop (TDB)
  --------------------------------   -----------------   -----------------
  tesla_s7                           2018-Feb-07 03:00   2048-Jan-01 00:00


texts: What are these objects on the night sky generally between 8:00 and 11:00 PM?

texts:
Many time I saw a moving star in the night generally been 08:00 to 11:00 PM. It is not any satellite, because it move in all directions, although it moves in a straight line. Sometimes from north to south, and sometimes from east to west and vice versa.

It is also not a comet, because its brightness is continuous, and it moves continuously in a direction. It is also not a plane ✈, because in the night a plane is travelling with three-four coloured light. And they generally do not move on the way of planes.

What are those moving stars?


texts:
Why are the Galactic Coordinates not aligned so that the Axes go through the Long Bar Y-axis aligned to it's longer side, positive with Sol, and the X-axis align to the center of the short length with Sol being in the negative? Z should obviously be on the galactic plane where it generally is I think...

I'm curious about whether there is a reason we shouldn't align it like this? It seems to make the most sense to me where as the current system, while I understand it, to me is just to Earth-centric, especially when we have something that stands out so much on the galactic scale you could use to figure out where you are with where as Where Sol is being 0,0,0 isn't really helpful to anyone unless you're already on Earth ^.^

The other part of my question is less "real" and more of a "I would like to know if there are any problems with doing this that I am unaware of" thing...

There are 3 question areas...

1
I use a unit I call a Lida, It is 24 terameters long and roughly equivalent to a Light Day.
On this map distances will be measured in Lida, more specifically, KiloLida.
1 Sector = $20 kL^3$
1 Block = $200 kL^3$
1 Grid = $2,000 kL^3$
1 Octant = $20,000 kL^3$

Each of the bigger areas contains 1000 of the next smaller unit down and can easily be referenced by 3 digits. So if I said Grid 346 that would reference the Grid in that Octant where each of those digits are xyz starting from the Galactic Center. Lower numbers are always closer, higher are always further from the Galactic Center.

Why not use parsecs and light years? They're really not practical to use. Likewise, AU are weird, and other units you either end up with very long numbers or poor conversions. Also with this unit, I find it very easy to work out distance and time in my head. The answer is 1.07% off, but that's not really an issue when you're not trying to be 100% precise.

Why use 20kL rather than 10kL or 1kL not many stars in that volume from what I looked at before so it makes sense to use that as division and it also divides up nice to the higher divisions.

2
I use another unit.

1 brut = $1*10^{19} kg$

The largest reason I'm using this is that scientific notation doesn't work in emergencies or common parlance so it makes sense to me to have a larger base unit when dealing with these larger scales. $1*10^{19} kg$, if I remember right (cuz I came up with this a few years ago and haven't used it since), comes from when the reference point numbers on the wiki for scale started getting fishy looking to me. Not a hard science thing, but seemed like a good place to have something like this.

3
This is the way I label Stars, planets, moons, etc... because it makes sense. I keep saying that, but you know, it's true ^.^

SO I - Star (or black hole)
SO II - Spheroid
          Brown Dwarf (Star?)
          Gaseous Spheroid - 12,000+ km radius and above (Most of its size is from gases)
          Terrestrial Spheroid - 1,500 to 12,000 km radius (Has a rocky mantle)
          Icey Spheroid - 200m to 1,500 km radius (Has an ice-water mantle)
SO III - Debris
          Asteroid - Comprised mainly of rock
          Comet - comprised mainly of ice-water

Child Star (?) - SO I that orbits a SO I
Planet - SO II that orbits a SO I
Moon - SO II that orbits a SO II
?? (currently also called a moon it seems) - SO III that orbits a SO II

SO means Stellar Object.
both SO and Spheroid are kinda bad names considering nothing but stars are Stellar and stars are Spheroids, but whatever, I think it gets the point across. Though I wish I could think up something better.

Anyways, do any of these 3 things create problems that I don't know about or that could cause a problem that I possibly can't see due to being a pleb in these matters?


texts: Can you see city lights on the Moon from Earth?

texts:
This is the opposite of another question. That question is about whether you could see cities on Earth if you were standing on the Moon.

Let's there are cities on the Moon and you're standing on the Earth on a clear night. Could you see the city lights?

If you're looking at Earth cities from the Moon, your line of sight is not affected by atmospheric turbulence because the Moon is airless. But if you are on Earth, then you have to look through the turbulent atmosphere to see faint lights. So you won't have to put up with the turbulence that makes stars look blurry or twinkley from the Earth.

But if you're on the Earth, any city lights on the Moon might look blurry or twinkley from our atmospheric turbulence. If it helps, imagine yourself at the top of a mountain so there is less atmosphere to look through and hence less turbulence.

In this picture of the Moon (and Venus in the background), imagine cities on dark part of the Moon's surface facing Earth. Those city lights should be easier to see than cities within the lit crescent.


texts:
I'm trying to understand following schema of the wikipedia page here.

Image subtitle is "Umbra, penumbra, and antumbra, for a lunar eclipse".

Distances and sizes are not to scale.

If distance Earth-Sun is about 150 Gm (gigameters) and Sun diameter is 1.4 Gm, $\arctan 1.4/150 = 0.57º$ (degrees). Thus, the Sun is seen from Earth with an angle of approx. 0.57º (0.01 radians). The Blue and red lines in schema should be near to parallel.

That means the point where umbra and antumbra touch is (being 12 Mm the approx diameter of Earth) at a distance of about $\frac{150}{1.4\times0.012}=1.3 \mathrm{Gm}$ from Earth.

As distance Earth-Moon is only 0.400 Gm, it seems impossible that Moon was never in the antumbra zone of the Earth.

I'm doing a basic error somewhere, but I do not know where.


texts:
I see this kind of projection of the celestial sphere into 2D frequently, usually with an image of the milky way galaxy or cosmic microwave background. This particular image shows the path of visible transits of the inner solar system planets across the sun as seen from locations outside of the solar system from the Motherboard article At Least 9 Exoplanets Could See Earth With Present-Day Human Technology which links to: R. Wells, K. Poppenhaeger, C. A. Watson, R. Heller; Transit Visibility Zones of the Solar System Planets, Monthly Notices of the Royal Astronomical Society, stx2077, https://doi.org/10.1093/mnras/stx2077

Question: What is the 2D elliptical projection of the Celestial Sphere called, and how can I make one? Is there a python-friendly package, but more importantly, is there a mathematical expression for this transform?


texts: What was the energy/wavelength/frequency of the CMB when first emitted/released?

texts:
Given the z redshift of 1089, and the temperature difference between then and now of about 1089, I tried scaling the ev, freq. and wavelength by 1089....
Is that right?
I get a freq. of about 240 Terahertz, 1.25 micron wavelength and almost exactly 1 ev of photon energy.....
Does that correspond to a blackbody
temperature of just under 3000 K?


texts:
Generally, the parallax is contributed to the motion of the earth around the sun. However, at the same time, the sun is moving too. It carries the earth with it. Presumably, the shift of the sun is bigger than the earth-sun distance. So, that will also cause apparent shift of a star in the background.

I am not so familiar with astronomy. Is my argument right?


texts: Radiative Flux, Irradiance and Luminosity confusion

texts:
First of all I know there is a similar question here, but I feel is wasn't answered at all.
My question is that I have seen many texts which says that Radiative Flux is equal to the Irradiance of a star. In Carroll & Ostlie book "An Introduction to Modern Astrophysics" even say that:

And Wikipedia's Irradiance on Earth's surface says this:

Average annual solar radiation arriving at the top of the Earth's atmosphere is roughly 1361 W/m².

Following this I first I assume that Irradiance and Radiative Flux are the same thing, but when searching for Irradiance on Wikipedia says that:

In radiometry, irradiance is the radiant flux (power) received by a surface per unit area.

Which means that Irradiance is Flux divided by Area, so Radiant Flux has units of J/s and Irradiance has units of W m^-2 which I remember from my Optics class, then again Carroll & Ostlie say that:

That doesn't mean if Irradiance is equal to Radiant Flux divided by Area, so F = I*A that would make Irradiance equal Luminosity / Area^2 ?
In that case the bolometric magnitude should be calculated with the integral of Irradiance, not Luminosity nor Flux right?
Probably I'm making it complicated for myself and it's not that hard to understand. I'm just sharing my confusion with you guys, please help me with that question.
Thanks in advance.


texts: Will Triton have a thicker atmosphere as the Solar System ages?

texts:
With an average temperature of around 34 kelvin, Triton is extremely cold. Currently, it has a thin mostly nitrogen atmosphere with a pressure of around 1 Pa. However, its surface has large deposits of nitrogen ice. This leads me to a few related questions.

Do we know how much nitrogen ice is on Triton?
If all the nitrogen ice on Triton thawed, how thick would its atmosphere be?
Will Triton thaw naturally, and have a thicker atmosphere, in the future as the Sun's luminosity increases?
If so, would its atmosphere be stable over a long period of time?
In the far future, perhaps as the Sun turns into a red giant, would Triton be warm enough to have liquid water?


texts: Calculating Relative Abundances to Solar For Explosive Nucleosynthesis Yields

texts:
I am having trouble deriving the abundance ratios for the ejecta products of a given supernova explosion model. From the explosion models, we are given the mass of 3 isotopes of every element produced in the explosion in solar mass units. I need to convert the mass of the ejecta products to number densities in order to solve for the abundance ratio. The abundance ratios for some element X with respects to silicon, with respects to solar values is defined as:
$[X/Si]=\frac{(X/Si)}{(X/Si)_\odot}$
Where X and Si are number densities.
If we consider for Oxygen: Using the solar values from Anders and Grevesse, where O$_\odot$ = 8.51e-04 and Si$_\odot$ = 3.55e-05 (abundances number relative to H). And using the explosion model 40A from Maeda+2003 (Table 2), we know the ejecta mass (in solar units) for:

oxygen-16 = 5.99
oxygen-17 = 5.33e-08
oxygen-18 = 5.48e-06
silicon-28 = 1.87e-01
silicon-29 = 3.57e-02
silicon-30 = 2.73e-02

How do we determine [O/Si]? Note, the answer should be 2.783.
My attempt at a solution:
$O = \frac{\text{ejecta mass of Oxygen-16}}{\text{atomic mass of Oxygen-16}}$
$O = 5.99~M_\odot / 15.994~amu$ (dominated by O-16; ignored the rest)
$O=0.3745~M_\odot/amu$
$Si=\frac{\text{ejecta mass of Si-28}}{\text{atomic mass of Si-28}} + \frac{\text{ejecta mass of Si-29}}{\text{atomic mass of Si-29}}+\frac{\text{ejecta mass of Si-30}}{\text{atomic mass of Si-30}}$
$Si=\frac{1.87E−01}{27.976} + \frac{3.57E−02}{28.976} +\frac{2.73E−02}{29.973}~M_\odot/amu$
$Si=0.008827~M_\odot/amu$
$[O/Si]=\frac{(X/Si)}{(X/Si)_\odot}$
$[O/Si]=\frac{(0.3745/0.008827)}{(8.51E−04/3.55e−05)}$
$[O/Si]=1.889$
Which is not 2.783. What am I missing?


texts: Which wavelength is the most quiet, for a ground-based radio telescope?

texts:
This might seem like a backwards question, but I'm interested in what wavelength to select in a (hypothetical) ground-based radio telescope observation to expect detecting as little as possible! :)

It should still be reachable from space, i.e. a wavelength with a high atmospheric absorption is probably a bad candidate.

I guess this could be answered by looking at a broad averaged spectrum collected by a radio telescope, and comparing against an atmospheric absorption spectrum chart.


texts: When is the belt of Orion slanted from right to left, going up? (Egypt)

texts:
I am trying to match up a detail of the Senemut ceiling to the time of the year it might involve. In the detail (shown below), the belt of Orion is slanted upwards from right to left:

Notice that the Orion Nebula is to the right. When I try to duplicate this in Stellarium, I can only get the belt to slant left to right, going up as shown below:

Is there some particular time of the year when the belt of Orion is visible from Egypt (Banî Suwayf) and slants upward going right to left, as in the Egyptian ceiling?

One answer below suggested that Orion's belt is like this when it rises, but I cannot duplicate it:

In Stellarium, I found by experimentation that Orion seems to rise on the morning of July 18th at the latitude in question and date range in question. However, as can be seen in the screen shot the belt still goes left to right.


texts: Why are galaxies distributed as walls and voids, or spider webs?

texts: I have wondered why the "walls and voids" of the cosmological galaxy distribution seem to resemble a "foam", like rising bread that's ready to fall, with "voids" corresponding to empty bubbles in the foam. James K and Rob Jeffers https://astronomy.stackexchange.com/a/18610/14485 seem to be saying local matter tends to relatively "overrule" the cosmological expansion, and that the bubbles ("voids") get relatively more cosmic expansion. This may explain the "foam" appearance: local large areas of slightly lower relative galaxy density will tend to cosmic expansion more, and will grow (less dense) more than denser regions, like bubbles in the foam, effectively driving all the galaxies into the walls between the bubbles.


texts:
Does the Moon have a night and day like Earth? When sitting on the Moon and viewing the Earth what does it look like when the Earth goes through phases like the Lunar Phase? How does the sun travel through the Moon's sky facing the Earth like this gif?

Part of my question was a duplicate so I deleted it and posted the other link below.
How bright is the full Earth during the lunar midnight?


texts:
I've learned about Orbits recently, and there are 6 orbital elements. Now, I've heard of three coordinate systems whereas, they can help you measure positions of stars in the night sky. The Altazimuth, the Equatorial, and the Ecliptic coordinate systems. Now, I can't quite grasp what they mean, and how to use them. This is what I am asking for from an answer to this question.
From night to night, I know that star and planet positions may vary, because we're rotating, and the start move due to it, and even in the day, we're still spinning, and the star positions keep changing, whether or not we can see them, or they're blocked by the sun's brightness, so the next night, they'll be in a new place. That being said, I don't want an answer that says there can't be a coordinate system that doesn't relate to my position on Earth, because I want an explanation for those three coordinate systems that includes my position (preferably using latitude and longitude).
Assuming this can be feasibly explained in a post, thanks in advance!


texts: How did the object CO-0.40-0.22 get its name, and how is it distinct from CO-0.40-0.22*?

texts:
There seems to be three things described in the recent Nature Astronomy paper Millimetre-wave emission from an intermediate-mass black hole candidate in the Milky Way:

Molecular cloud CO–0.40–0.22 with an extremely broad velocity width, near the centre of our Milky Way galaxy.
a compact object with a mass of about $10^5 M⊙$ is lurking in this cloud.
a point-like continuum source called CO–0.40–0.22*

Question: What are the objects CO–0.40–0.22 and CO–0.40–0.22* and what is the difference between the two. How did the originally discovered CO–0.40–0.22 get its name?
The news of the paper is described in the Science item Long-rumored midsized black hole may be hiding out in the Milky Way.
There is a nice writeup in Gizmodo for lay scientists: Astronomers Think They Discovered The Missing Link in Black Hole Evolution
The paper is not paywalled and can be read here: https://www.nature.com/articles/s41550-017-0224-z.pdf

Abstract:
It is widely accepted that black holes with masses greater than a million solar masses (M⊙) lurk at the centres of massive galaxies. The origins of such ‘supermassive’ black holes(SMBHs) remain unknown, although those of stellar-mass black holes are well understood. One possible scenario is that intermediate-mass black holes (IMBHs), which are formed by the runaway coalescence of stars in young compact star clusters merge at the centre of a galaxy to form a SMBH. Although many candidates for IMBHs have been proposed, none is accepted as definitive. Recently, we discovered a peculiar molecular cloud, CO–0.40–0.22, with an extremely broad velocity width, near the centre of our Milky Way galaxy. Based on the careful analysis of gas kinematics, we concluded that a compact object with a mass of about 105 M⊙ is lurking in this cloud. Here we report the detection of a point-like continuum source as well as a compact gas clump near the
centre of CO–0.40–0.22. This point-like continuum source (CO–0.40–0.22*) has a wide-band spectrum consistent with 1/500 of the Galactic SMBH (Sgr A*) in luminosity. Numerical simulations around a point-like massive object reproduce the kinematics of dense molecular gas well, which suggests that CO–0.40–0.22* is one of the most promising candidates for an intermediate-mass black hole.


texts: Are there any galaxies visible in the night sky around the Orion constellation?

texts:
I'm writing a story for NaNoWriMo, and in it there is an extraterrestrial race whose home galaxy is visible from Earth. This home galaxy is visible (or even partially visible or barely visible) in the night sky as a close neighbor to the Orion constellation. "Close neighbor", as in "within or around" the Orion constellation.

Is there any such galaxy?


texts:
I have heard of years with longer summers and winters and shorter springs and falls and vice versa because of a change in the earths axis.

Is this from the procession that causes the season switch every 25,800 years or is it from some other change in the earth's axis like angle change and not revolution at the same angle(which I think the procession is)?


texts: Can we tell how fast bodies are moving away by measuring their frequency?

texts: It's clear the universe is expanding because light from distant bodies, like galaxies, are shifted towards the red side of the spectrum.  In other words, the light measured is more red than it should be when compared to laboratory results.  This is great for measuring the distance to other bodies, but can't we also measure their velocities of departure by measuring how fast the light from these bodies is becoming more and more red over time?  That is, v is directly proportional to the change of frequency divided by the time elapsed?


texts: Do all stars have an Oort cloud or is it a rare occurence?

texts: Do all stars have an Oort cloud like ours that will be filled with comets and other objects? If not, why are they not around every star?


texts:
The luminosity of a black hole accretion disc gaining mass at a rate $\mathrm{d}M\over \mathrm{d}t$ can be estimated as

$${1\over 12}{\mathrm{d}M\over \mathrm{d}t}c^2$$

That is a substantial proportion of the rest mass of the in-falling matter. The linked document explains that the factor 1/12 is because at less than 3 times the event horizon radius the matter "spirals in without
radiating more energy"

What causes matter in the accretion disk not to radiate beyond this limit? It is twice the radius of the photon sphere, is the reason general relativity?


texts: Calculate the orbital phase when plotting the Radial Velocity data of a transitting exoplanet

texts:
I'm not quite sure how I find the orbital phase  ($\phi$) of a transitting exoplanet. For example, I have this RV data in this article:

First of all, I don't know how that phase or "cycles" is derived. But that's not the phase $\phi$ I'm looking for but this (in the same article):

As you see, that phase goes from 0 to 1, and I know it has to do with the time of passage from the periastron and the data time (the HJD column), but I'm not able to derive this number in the interval [0,1]. So, if we assume the orbital parameters are known, how can we derive that number?


texts: What is the relative velocity between planets in different solar systems?

texts:
Is it possible to estimate what the difference in velocity is between the earth and another convenient exoplanet? Or perhaps just our star and a near neighbour?

I'd be curious where I could find the figures, and I'm wondering exactly what the magnitude of the difference is between relatively near neighbours.

Context:

Putting together an outline for a book, and I'm curious about something.

In the book, faster-than-light travel happens through instant travel between two points in space. In doing so, you retain all of your kinetic energy. This means you'll emerge at your destination with the same velocity as you had before you transitioned.

The bulk of the travel time in interstellar travel would simply be matching velocity with your destination before transition - the vast majority of the distance of the journey would be instantaneous, since for traffic control reasons ships are expected to come in at a reasonable speed when compared to their destination.


texts:
India is going to launch a spacecraft to the moon on 16 July which will consist of a lander, an orbiter and a rover. I found an article in today's newspaper regarding   this. If you zoom in a bit, you will be able to see the list of other lunar missions that have taken place over the years. A common difference that I found in lunar missions of 20th century and lunar missions of 21st century was the time. Earlier, the spacecrafts reached moon in a day or two but recent missions take over 2 months.

With developed technology, it should take even less time, but it's the other way round. Can anyone explain the reason behind this.


texts: Is gravitational energy released when a body contracts?

texts: Kelvin stated that gravitational energy released due to contraction was responsible for the energy radiated in the stars. Although the theory was wrong, was the assumption practically right? If it's right, how does contraction take place?


texts: Why is our solar system "tipped" about 63° with respect to the plane of our galaxy?

texts: Our own solar system is "tipped" by about 63 degrees with respect to the plane of the galaxy. Has it ever been researched or is there any scientific theory which could explain the reason why our solar system and solar systems in general are not "in-line" to the galaxy's plane? What exactly determines the orientation of solar systems?


texts: What is the specific heat capacity of interstellar clouds?

texts:
Star forming molecular clouds and especially Bok globules are low temperature $\sim 10 $ K environments with density on the order of $10^{-18}$ kg/m$^3$, mostly hydroogen with about 1% dust. What is their heat capacity?

I have tried to find good data for low-temperature heat capacities for hydrogen (which would be nice to have anyway), but most experiments also use dense hydrogen rather than the by Earth standard very low-pressure molecular gas of the clouds. Are there any decent estimates of how much a given increase in energy increases the cloud temperature? Or should one just use the ideal gas approximation for a diatomic gas and assume $C_v\approx (5/2)R$ per mole?


texts: Binary star system effects at the barycenter

texts: I haven't been able to find anything on this so far. Using Alpha Centauri as the study, what events/effects ( if any ) would happen between the two stars? More specifically, between the gravitational fields converging and the stellar winds, would there be anomalies that form between the two such as a nebula or cloud of charged particles that shimmer/bounce around because of the gravitational forces meeting.


texts:
Given our real solar system how would planet orbits plot look like if we fix earth in the middle (put earth in the middle and draw a real orbit of a given planet) ?

What would be the shape of its orbit? Is there any software that allows you to do such plot ? Does anybody have an example of it ?

I have tried searching for such image but most results are connected with historical theory .


texts: Why are solar telescopes built on lakes?

texts:
The telescope big bear is located in the Southern California.
According to the wikipedia page, water can cool the observatory.
Is it better to build it on a cold high mountain with stable and clear atmosphere?
What is the difference when building a solar and an optical telescope?  Optical telescopes are usually not build on lakes.


texts: Why does the Moon's terminator look "wrong" in this image?

texts:
There is a picture of the moon in National Public Radio's on-line article Get Ready For Halloween By Watching The Moon's 'Occultation' Tonight. It looks wrong to me - specifically, the brightness gradation near the terminator - or lack thereof.

The image is credited "A waning gibbous moon occultation will be visible Tuesday night in parts of the United States. JPL/NASA" but I wonder if this is true. Something just looks "wrong" here.

In the original article the JPL/NASA contains a link to this page, which currently contains this image also shown below. It looks more like an actual photograph.

And here is a NASA/JPL image from https://svs.gsfc.nasa.gov/4404 for 2016-10-19 04:00 UT, which if I uderstand correctly is not actually a photograph, but simulated from LRO data. It also illustrates that the terminator is expected to be graded from light to dark and contain contrast from shadowing.

above: terminator from all three images. Realistic terminator on the right show graded intensity and strong shadowing from the highly oblique incident light.


texts: Extra-solar identification of binary planets

texts: Pluto and Charon orbit about a common barycenter that isn't inside of either planet. Let's assume that this relationship was scaled up to the point where it could be detected by a search for extrasolar planets. Could any of the methods we currently use tell us the difference between one massive body vs two bodies of nearly identical mass?


texts: How does the orbit of a 2-body system evolve as it orbits a more massive 3rd body?

texts:
I have been reading up on how multiplicity of star systems decline with star mass, which implies a relatively common occurrence of binary star systems orbiting more massive stars. I would imagine this would also mean the orbital plane of such multi-star systems aligning with the orbital plane of the system and the star it orbits as time passes, which I believe is in line with how disc accretion is such a common pattern.

What I am wondering is how such a realignment would affect behavior of the orbit of a hypothetical binary system? Would the stars get closer to the barycenter or further as this realignment occurs? How about periodicity or heat?


texts: How to choose between methods to resample/interpolate ephemeris state vectors? Are there recognized techniques for orbital data?

texts:
I have ephemeris data for state vectors of a satellite in a J2000.0 coordinate system. This data is already filtered and cleaned.

The data sample rate ranges between 1 second and 60 seconds, and I want to resample the data down to <10 milliseconds with a constant, regular time step.

I have already managed to interpolate using methods from scipy.interpolate with cubic interpolation; interp1d and griddata.

This leads me to the question of how to choose between various methods to resample/interpolate ephemeris state vectors. Certainly the interpolation of tabular ephemerides is something that astronomers and orbital dynamicists need to do and so there must exist some guidelines or best practices or recognized-better or -worse ways to so this.

Question: How to choose between methods to resample/interpolate ephemeris state vectors? Are there methods recognized as superior for orbital data?


texts: Can we see the Big Bang happen if we look far enough?

texts: The observable universe is constantly expanding as more light from the Big Bang reaches us. This light has been travelling for billions of years, so we are looking at the universe as it was a few billion years ago. This being said, would it be possible to look at the Big Bang in action by looking deep into the universe?


texts: Calculate time when star is above altitude 30°

texts:
To find the best observation time for an object, I'd like to calculate the time when it is 30° or more above the horizon. Local Sideral Time would be sufficient.

To include that in my program, I need the formula.

Example:
On June 4th, Jupiter has the coordinates
RA= 9h 19m 28.0s
Dekl= 16° 32' 0"

It rises at 10:32 and sets at 00:05.

After rise, when is it at altitude 30°, and after transit, when is it at altitude 30° again ?

I found this formula at http://www.stjarnhimlen.se/comp/riset.html. Although it's for the sun, it seems to be what I'm looking for.

$$\cos (\text{LHA}) = \frac{\sin (\text{h}) - \sin (\text{lat}) \times \sin (\text{Decl})}{\cos (\text{lat}) \times \cos (\text{Decl})}$$

Applied to the sample assuming a latitude of 45° I get.

Is this the correct approach?


texts: Is Earth the perfect place for life ? If it isn't then how could conditions be better here ? For example, the size of the Planet, our atmosphere, distanace from our Sun etc.


texts: Why do some artificial satellites decrease and increase in brightness multiple times?

texts: I just observed a satellite almost directly above me travel for a few minutes while constantly dimming and then getting brighter. It did this for about 3 minutes until it faded out. I also observed a satellite with similar behavior on July 4th. I was thinking the satellite might be rotating, but I do not know of any satellites that rotate. Then I thought it could be a piece of space junk, but I don't think they get big enough to be visible from the ground. Does anyone know why the brightness of some satellites change while others remain constant? I am in the Northwest of the US. (Northern hemisphere)


texts: Titan, which is smaller than Mars, has an atmosphere but Mars is not able to maintain its atmosphere. Even Luna (the Moon) doesn't have an atmosphere. Why is Titan able to hold an atmosphere, despite being smaller than Mars?


texts: Comoving distance between two points [(RA1, Dec1, z1) and (RA2, Dec2, z2)]

texts:
I have Redshift (z), RA and Dec positions for two points in a galaxy catalogue (say P1 = [z1=4, RA1=140, Dec1=2] and P2 = [z2=6, RA2=150, Dec2=5], where RA and Dec are given in degrees). How can I find the comoving distance between these two points using any package in python (like AstroPy, CosmoloPy etc)?

I am assuming a Flat-LCDM model with the cosmology H0=70, Om0=0.3, Ob0=0.05.

Presently, I am using this:

import cosmolopy.distance as cd
cosmo = {'omega_M_0' : 0.3, 'omega_lambda_0' : 0.7, 'h' : 0.70}
cosmo = cd.set_omega_k_0(cosmo)
z1 = 4.0
z2 = 6.0
d_co = cd.comoving_distance(z2, **cosmo)

Specifically, my questions are these:

(i) In the said example, how do I use information of the starting redshift z1?

(ii) Do I need to use information of [RA1, Dec1] and [RA2, Dec2] for an accurate calculation of the comoving separation between P1 and P2 (I need to find the comoving distance to a great degree of accuracy)?


texts: Is the newly discovered exoplanet 'Teegarden b' habitable?

texts: A new exoplanet has been just discovered around the star Teegarden, at only 12 light years away.


texts: How do we determine something is "x" light years away?

texts: I always read/hear "This galaxy is X thousand light years away" or some similar statement (for example see this table). Please excuse the naivety of question. How do we determine that some astronomical body is "x" light years away. Surely we don't send light beams and wait for them to come back. :-P


texts: What would Aurora look like if no magnetic field was present around the Earth?

texts:
The greatest part of the Earth is protected from the Solar wind by its magnetic field. This field makes the wind particles (mainly protons and electrons) the beauty of Aurora appear.
Suppose the magnetic field wasn't present. The Solar wind particles hitting the southern and northern parts of our planet would distribute themselves over whole the Earth's surface.
How would Aurora look like?
For certain it would be not slowly swirling (following the slowly changing magnetic field lines). Will we see a sparkling sky? Or what?


texts: How does the Sun's gravity have so much force and pull on the solar system? How does it scale?

texts:
Watched this video: https://fb.watch/1U0vCFBr0L/
Ok, so the distances are huge. And the sizes are much different. But I wonder how then the sun keeps the planets etc. orbiting it. If we swap out all those objects in the video (soccer ball for the sun, grapes, pin heads, etc.) for equivalently sized balls of iron, equally dense objects, they would have a negligible pull on each other.
A ball of iron the size of a football could never keep a grape 4 football fields away orbiting it. Or could it? Is gravity proportionate? At larger star and planet sizes, it pulls harder?
What is the explanation here?


texts: Does Uranus have a stronger gravitational pull on its moons than Earth does?

texts: I've read that Uranus has a lower surface gravity due to its lower density than Earth. However, does this mean Uranus has a weaker pull on its moons than Earth does for the same reason?


texts: Why do astronauts move so slowly in zero gravity?

texts: When astronauts are floating about in a spaceship or space station, they nearly always move very slowly. After doing a bit of research I can't see why being in zero gravity would restrict movement to such a degree. It's almost as if there's resistance to their movement, like they're moving through water.


texts: Why are M dwarf stars the most active (in terms of starspots and faculae) of all stars?


texts: Day and night temperature on an earthlike planet with longer rotational period

texts:
I'm trying to understand the climatic effects of the far future scenario of an Earth-like planet with a reduced rotational speed caused by tidal locking with the moon (day-night period of 28 days, one hemisphere always facing the moon, the other never facing the moon).

I understand that observations of the moon's surface temperature have shown day temperatures of 120°C and freezing cold nights of -230°C.

How would the day and night temperatures of tidal locked Earth vary?

I am also interested in climatic effects caused by the reduced tides, coriolis force, increased evaporation, but this may reasonably be outside the scope of this question and it's answers.


texts: What was the nature of the signal received from the direction of HD164595?

texts: There's been a story in the news recently of a potential SETI candidate signal received from the vicinity of star HD164595.  What's the nature of this signal?  Is it a single pulse of energy, or does it change over time?  Can someone point me to a link or paper than shows it in more detail?


texts: how to calculate the star formation rate (simplified) for a galactic model

texts: we are (programming summer project Y10-11) making a very simplified model of a disk galaxy. would love to know if there's a simplified equation for the average star formation rate of the stellar disk based on the stellar mass and radius of a given circular disk galaxy.


texts: How to calculate the orientation of planets at current epoch

texts:
For an application I am working on I am creating a simulation of the solar system. In this simulation, a user needs to be able to 'move' to any position on any planet, and have the sky be accurately simulated around him.

Using the examples & calculations provided at http://stjarnhimlen.se/comp/ppcomp.html and the data provided at https://ssd.jpl.nasa.gov/txt/aprx_pos_planets.pdf I am able to compute the POSITIONS of the planets at any date, however, what I am still looking for is the ORIENTATION of these planets at that position (i.e. which way is Long 0 Lat 0 pointing, and which way is Long 0 Lat 90 pointing (with respect to the vernal equinox)). I need this orientation in order to figure out what the rotation (quaternion) of this planet needs to be..

I have been looking around, but have so far not been able to find a source for any kind of information like this. The closest I've found was https://en.wikipedia.org/wiki/Poles_of_astronomical_bodies , but that only gives me an up-vector, not a 'forward' (and is for J2000, not the current Epoch).

Can anyone be of assistance?


texts:
Arp 299 is in the news, with most sources reporting it as 140 or 150 million light-years away. But what kind of distance is this?

The paper which is trhe source for the news item has Supplementary Materials which mention the distance but don't appear to say what kind or give details:

  The merging pair of galaxies Arp 299 (Fig. 1) at a 44.8 Mpc distance (33; corrected to the cosmic microwave background reference frame; H0 = 73 km s^-1 Mpc^-1) is one of the brightest nearby LIRGs with an IR luminosity LIR ~ 7x10^11 L_⊙ (34; L_⊙ = 3.833×10^26 W).

Is it obvious what method is used (and thus what type of distance this is) to measure the distance to this galaxy? Is there a standard reference/database/etc. giving basic information like distances of astronomical objects like galaxies? I'd like to know the answer for this galaxy, but answers that generalize will naturally be more interesting.

Edward L. Wright has a cosmology calculator that is useful in converting between different types of distances. His page on distances gives many methods for measuring distances; I feel that if I knew which type (if any) of these methods was used to find the distance I'd have a decent chance of figuring out what kind of distance it was (and could find the other distances by bisection).


texts:
I have a Celestron Astromaster 130 EQ. After aligning  my telescope's polar axis with Polaris, in order to track stars I need information about the coordinates in terms of right ascension (RA) and declination.
But in all the astronomy apps I have found that they have fixed the RA and declination coordinates and are tracking stars with respect to azimuth and altitude.
How am I supposed to use this data? Please help!


texts: Fast moving stars at equal distance in straight line 18.04.2020 evening

texts: Yesterday, I have observed fast moving bright stars at equal distance in straight line (18 March 2020) in Germany around 20:00 in night. I was facing the east direction. What could be the reason for these symetrical moving stars?


texts: If any object could become a black hole, could any object become a neutron star?

texts:
A black hole doesn't necessarily need to form from a star; theoretically, it could form from any extremely dense object. In fact, many astronomers differentiate certain black holes, like supermassive ones, from stellar ones (ones that form from stars).

However, could the same apply for neutron stars? Neutron stars only form because of the intense gravity during a star's collapse: electron capture is forced to happen, and the majority of the star becomes neutrons. Could this potentially happen to non-stellar objects, if the gravity forces electron capture?

If so, why don't we see as many of these "neutron objects" as we do non-stellar black holes?


texts:
This is being asked from a lay-person point of view. However, please do not hesitate to give more detailed answers that require prior knowledge - if these answer the question more accurately.

My confusion currently comes from the fact that everything in the universe is moving in some way or another - so any reference point we use would also be moving/not completely reliable.

As such, how can we accurately determine that we have completed an exact 360 degree rotation around the sun (and as such, measure exactly how long it took)?

To be clear, this is asking about how we can determine that we have completed a single 360 orbit of our sun, and not the timing aspect of how we know how long a second is. If this situation is different for measuring the orbits of other bodies around their star - it would be great to expand on those differences as well.


texts: Divide a star catalogue to optimize star search

texts:
I'm continue working on my Planetarium software and I have a doubt.

At this moment my star catalogue is very small, but I'm planning to use a bigger one. To optimize the search inside this catalogue I think I have to divide it in regions.

These regions will be delimited by right ascension and declination.

Using stars' right ascension and declination, how can I divide the sky to optimize my search?

I want to retrieve all stars visible at this moment. Maybe not all of them, only the visible by the user. For example, if user is looking to the North, he/she won't see the stars at the South. The region will be the area visible by the user at this moment, and I want to get all stars for that given region using also a limit magnitude.


texts: Is there a good replacement finder scope for the Celestron 127EQ?

texts:
I've had a Celestron 127EQ for a couple years now and have only used it a couple times.
One of the reasons I haven't gotten much use out of it is that when I do use it I spend all of my time aligning the finder scope. Every time I so much as breath on it the alignment is gone.
It already takes me a good while to line the scope up once and then as soon as I try to target something with it I inevitably brush some part of my face against the finder scope and have to start over with the alignment.
I'm happy to buy a new mount and/or finder scope, I just have no idea what to get that won't be just as bad.


texts: Why planet's orbit is not perpendicular or random ? It always seems each planet is revolving on the same geometric-plane around the star.


texts: Is there any other theory, apart from the Big Bang paradigm, which describes the birth of universe?

texts: The Big Bang theory is the approved theory of the "birth" of Universe. Are there any other theories which can explain how our Universe came into existence?


texts: Question about finding energy density of a fermionic-bosonic gas

texts:
We know that energy density is given by this formula:

$$u = \frac{1}{V}\int_0^\infty\epsilon_pf(\epsilon_p) g_s V/h^3 4\pi p^2 dp$$

Where $\epsilon_p=pc$ for relativistic particles. also $f(\epsilon_p)= \frac{1}{\exp((\epsilon_p -\mu)/kT) \pm1}$ where minus is for bosons and plus is for fermions.

Now if we evaluate this for photons which have $\mu =0$ we get
$u = aT^4$ where $ a= 4 \sigma /c$ is radiation constant.

If electrons and positrons are in equilibrium with photons (so $\mu = 0$ and $g_s =2$) We will get $u=(7/8) a T^4$

equilibrium equation:
$\gamma + \gamma \iff e^+ + e^-$

Now think we have electron+ positron + three types of neutrinos + three types of anti neutrinos which are at all in equilibrium with photons. $g_s=1$ for neutrinos and anti neutrinos. now how can we get an equation for energy density? what we must use for $g_s$?

I am also not sure about $u = (7/8) aT^4$, Is it the energy density of electrons or positrons (so the total energy density is $2u$) or energy of both of them is in this equation?

Note: All of the particles are relativistic. These question conditions is for early universe.


texts:
Supposedly, if humans were to establish a colony on one of the moons of a planet (such as gas giants in our own solar system), how could we possibly design date and time system? On Earth, we define date based on rotation about Sun and time on Earth's revolution. But, with a moon of another planet, this will add another factor to date/time system. So, how can we cope with this?

PS: I am not sure about what tags this question should carry. Feel free to correct them.


texts: Is it possible (for either a satellite or a planet) to orbit around a black hole? Do they attract everything around themselves into the center? Or they just affect gravitational force just like stars?


texts: Is extraterrestrial mining more difficult or impractical for bodies without plate tectonics?

texts:
This article talks about the possibility of mining Uranium on the moon. Since the Moon lacks the geological forces that have created veins of concentrated minerals on Earth, would extraterrestrial mining be more difficult or impractical? How does Moon, Martian, or asteroid mining overcome the lack of mineral veins otherwise formed by Earth's geology?

It seems like extraterrestrial mining would be at least as difficult as trying to refine desert sand, which isn't a thing.

A short video on how gold veins form

Wayfaring Stranger added an interesting link on ore genesis.


texts: Can you see the difference with the naked eye whether Venus is at the other side of the Sun or at the Earths' side?

texts: When Venus is at an angle with the Sun from the Earth's perspective we are able to see the reflection of the Sun on Venus. But imagine that Venus is on the farthest half of its orbit around the Sun. In that case the planet is further away but we receive his reflection on a larger plane. So could an eye see the difference whether Venus is further away in his orbit or closer to the Earth?


texts: What day/night cycles, climate and seasons would experience Alpha Centauri Bb inhabitants?

texts:
Alpha Centauri Bb is an exoplanet orbiting Alpha Centauri B. It is asserted that given the close distance to the star the planet should be tidally locked.

The orbiting period of the planet is about 3.2 days.

If the planet has no atmosphere (which is very possible due to proximity to the star), its dark side should experience low temperatures like permanently-shadowed areas of Mercury do.

At the same time the planet is about 11 AU from the other star, Alpha Centauri A.

This possibly means that the planet should experience quasi-day/night cycle each 3.2 days.

My questions are:

To what temperatures the dark surface of such planet could be heated? Is there possibility of liquid water?
Will the radiation of the second star be enough to provide normal day-like illumination and heating?
Will the calendar on such a planet differ sufficiently from a calendar of a planet that experiences day/night cycles from the nearest star?
Will such planet experience seasons and how they would be arranged?


texts:
I have seen pictures of clusters of galaxies, usually used in regards to theories of dark matter and galaxy formations. One of the most famous ones has the perceived shape of a stick-figure. If I am not mistaken some of these clusters seem to be bigger than our observable Universe horizon of $14$ billion light-years, which is as far as we can see because of the age of the Universe.

My assumption is that these are just coordinates plotted into a computer simulation. However, are these clusters the size of our observable Universe horizon or are these more theoretical abstractions?

EDIT: Interesting new find on the subject. Laniakea Supercluster.


texts: Is there a webpage that shows the night sky but can filter out dim stars?

texts:
This webpage is very good for viewing the night sky and learning the names of the stars
Timeanddate - Astronomy
However, it shows too many stars. Because I live in the city, I can only see about 50 stars. If I could filter out all of the dim stars, that would help me focus on just the top 50 brightest stars. If I want to learn the names of the stars and how to identify them I have to start with the brightest. Yes, you can scroll over the star and it will tell you how bright it is, but that is very time-consuming.


texts: What is the specific term for time of the night when there is no moon?

texts: There are times when the sun goes down and it takes a while for the moon to rise, because the moon obviously doesn't rise with the sunset whole year. I guess this happens only when the moon is full. Also, in some days, moon sets in the midnight and there is no moon on the sky for the rest of the night. So, I was wondering what that time period of the night is called when the moon has gone down, or has yet to rise? Can we call it 'moondown'? I am not talking about the new moon when there is no moon the whole night. Please help, and thank you in advance!


texts: The ratio for a planet to be tidally locked has to be 1:1, but the ratio for Mercury is 3:2. How is Mercury tidally locked if the ratio is not 1:1?


texts: What is the farthest reported distance from observer from which a solar system body has occulted a star?

texts:
I originally wrote "...farthest distance from Earth..." but changed to "observer" in case the occultation was observed from a space telescope. It may not matter much but I didn't want to over-constrain or burden the answer.

The occultation of a roughly 13th magnitude star by a roughly 40 km diameter object in the Kuiper Belt; 2014 MU69 has been successfully observed! I'm hoping to be able to look up the star's name direct. On 2017-Jun-03 03:07 UTC it was about 43.294 AU from the Sun, and 42.435 AU from Earth, (using the JPL Horizons ephemeris.)

I'm wondering if this is the farthest distance from which a solar system body would have been seen to occult a star?


texts: What is the "lost light" in this unusual Hubble Deep Sky image?

texts:
The Daily Galaxy article “The Lost Hubble” –New! Deepest Image of the Universe Ever Taken says:

  To produce the image a group of researchers from the Instituto de Astrofísica de Canarias (IAC) led by Alejandro S. Borlaff used original HUDF images from the Hubble Space Telescope. After improving the process of combining several images the group was able to recover a large quantity of light from the outer zones of the largest galaxies in the HUDF. Recovering this light, emitted by the stars in these outer zones, was equivalent to recovering the light from a complete galaxy (“smeared out” over the whole field) and for some galaxies this missing light shows that they have diameters almost twice as big as previously measured.

The image looks really strange, what is going on? Is there a technical article associated with this work?


texts: What are evidences of stationarity of rotation of galaxies

texts:
Recently I have found the article Does There Really Exist the Problem of the Dark Matter in Spiral Galaxies? which states that dark matter does not exist because astronomers are wrong assuming stationarity of galaxy rotation.

According to them Doppler measurements give only one component of speed which is insufficiebt to restore full three dimensional vector. So they claim that stars in galaxies are on escape tragectories but reproduce correst rotational curves if we assume stationarity of rotation.

What are evidences that this is not true, what about measurements of proper motions, not doppler shifts only?


texts: As has been pointed out by some scientists, that black holes aren't stable bodies but are eternally collapsing objects. How does one come to such a conclusion? Is hawking radiation related to this in some way?


texts:
The universe is expected to have a time when star formation slowly ceases. However, this seems bizarre as there is always an abundant amount of matter in the Universe. Massive amounts of hydrogen exists in several galaxies, but they are deemed dead. Any gravitational disturbance can send the gas into a protostar, and even if there weren't hydrogen left, enough helium or carbon can turn a star into a star that fuses heavier elements, until the universe is depleted of such and mostly elements heavier than iron.

So why does star formation cease when these is still abundant hydrogen around? Is there some sort of interaction in these hydrogen supplies that prevents star formation? Is the gas kept at a temperature that is too hot for formation? Or have I made a misconception?


texts: What study profiles could land me the job of astronomer?

texts:
I realize there are very few to none universities that offer direct specialization of astronomy. If I aspired to be make astronomy my career choice, I'd likely have to pick something like physics and specialize later - or something similar - but that's just my hunch, and I'd prefer to know for sure.

What educational and professional paths optimize one's education and skill set for the occupation of astronomer? How do I become one?


texts: If we stood on the surface of a Jovian moon, Saturn would appear as a dot. Why doesn't Saturn appear like this in a telescope?

texts: Images from the conjunction like these show Saturn just a bit smaller than Jupiter. However, if you were in the vicinity of Jupiter, Saturn would still appear as a dot to the naked eye, wouldn't it? If so, why is Saturn recognizable as a planet through a telescope in which Jupiter is also seen as a planet? As if they were actually very close to each other, at about the same distance from the Sun. I mean, if you recognize Jupiter in a telescope, shouldn't Saturn behind it look like a dot, unless you have a much, much larger zoom in which Jupiter would appear too close to match into the whole image while being too unsharp anyway?


texts: How can the next supermoon be analytically predicted?

texts:
The lunar motion can be predicted with basic celestial mechanics, but the perigee and apogee are not always the same, basically because the attraction of the Sun makes some oscilations in the semi-axis of the orbit (https://en.wikipedia.org/wiki/Perturbation_(astronomy)).

My question is: how do they know when the full moon will get as close as it got in the recent supermoon? For example, the Dailypost article Biggest Supermoon in 68 years will light up the November sky claims that the full moon won't come this close to Earth until November 25th, 2034.
How do they kow that? Are they using the perturbation theory equations to predict this? If so, can anybody give me some source or explanation of how it's done analytically?


texts: The furthest horizon in the Solar system

texts:
Where can I observe the furthest horizon in the Solar system ? And what the length of it ?
The furthest horizon on Earth can be observed from mount Everest ~ 336 km, On Mars - from mount Olympus ~ 386 km.

Edit: If the walls of the Rheasilvia crater can be seen from the opposite sides (it appears so) you can see the surface as far as 505 km.


texts: Naive star filter visible at night in certain country

texts:
I have a HYG catalogue and I'd like to filter out stars visible at night and in Europe.

Doesn't have to be exact. I was assuming that it'll be all stars with positive declination, but I wasn't sure about RA values.

Thanks, Michal


texts: Is atmospheric turbulence irrelevant for ExoPlanetary transits and radial velocity measurments?

texts:
Atmospheric turbulence is known to scatter photons in a quasi-random way along their path throughout the atmosphere, resulting in lower imaging resolution than would have been anticipated by instrument-only considerations.

I have been thinking whether the same effects can play a relevant role in limiting the sensitivites for photometry in transits or for spectrometry in radial velocity measurments.

My thoughts so far:

Transits: as I'm no observer I don't know if atmospheric turbulence is actually strong enough to scatter source photons out of the line-of-sight, rendering them undetected. This would fiddle with the signal-to-noise ratio per measurment and would let it fluctuate over time.
Radial velocity: Turbulence should be able to influence a spectral measurment from the ground, if the induced turbulent broadening is significant compared to the line width that can be resolved with the instrument considered. Taking the turbulence-induced doppler shift $\Delta v/c$ as $10cm/s /c \sim 10^{-7}$ (I assumed turbulent eddy-velocities to be comparable to typical winds) as typical for Earth's atmosphere, this should be  insignificant even for a high-resolution spectrograph like HARPS that has $\lambda/\Delta \lambda \sim 10^5$.
However smaller eddies rotate faster, they could thus reach the detectability range when $\Delta v/c \sim 10^{-5}$

Here my expertise in this topic ends, and I'd hope for someone from this community to illuminate the points above. Also googling usually only points to the benefits in direct imaging.
Bonus question: Would adaptive optics always help to remedy any issues that might arise?


texts: What would be the obstacles to building a 6.5km space telescope besides cost?

texts:
In the comments of another question on this Stack Exchange site, I talk with another user about the possibility of building an optical space telescope with a 6.5 km aperture.

Obviously, this is much larger than any rocket we have constructed, so it would need to be launched from Earth in a number of components and assembled in orbit in a similarly massive number of spacewalks, and the sheer scale of it would likely require active heat management systems to prevent heat expansion of the components from sunlight warping the mirrors or stretching the distance between the mirrors.

Are there any other obstacles that would prevent this project from being possible?


texts: The black hole binary that was detected by advanced LIGO - how do such hypergiant binaries form?

texts:
With today's announcement of the historic detection of gravitational waves from the merger of 36 solar mass and 29 solar mass black holes 1.3 billion light years away, one can not help but wonder how such a black hole binary system was formed.

Has there ever been any observation of a hypergiant (class 0 or Ia star) binary system in the optical or other EM radiation? I would expect that these observations would be rare give the short lifespan of these stars.

If a black hole binary formed from a binary of population 3 stars with masses over 600 solar mass, how long would one expect that they would remain in orbit around one another before they merge?


texts: What is the physical reason of the mirror principle in the stellar evolution?

texts:
I understand that stars transition into the red giant phase by obeying the mirror principle, as written here:

  Shell-burning stars obey something called the mirror principle, which is an observation gleaned from the models that when a shell contracts, the envelope of the star will expand and vice versa.

However, I read that this information was gleaned from observation. Could anyone explain the reason or the physics behind why this happens?


texts: How is it that all planets (and moons) in our solar system are in equilibrium orbits?

texts:
Previously, I was told that in order for any bodies to orbit each other for over a long period of time, the orbital period, distance and masses have to be precisely matched such that the bodies won't eventually collide and forming larger bodies or being swung out of orbit.

How is it then, that all 8 planets (and countless dwarf planets), and their moons, and the Sun are all in such equilibrium for over thousands of years (if not millions)? Could it be possible what we see today are what's left, i.e. countless planets or moons have been swung out of the Solar System and collided, until a stable (relatively speaking) system is reached as we observe today?


texts: Why is the difference from a perfect sphere the same for the Earth and the Moon?

texts:
Wikipedia gives the following physical dimensions for the Moon:

  Physical characteristics

Mean radius        1737.1 km  (0.273 of Earth's)
Equatorial radius  1738.1 km  (0.273 of Earth's)
Polar radius       1736.0 km  (0.273 of Earth's)

In all cases, the proportion of Earth's equivalent measurement is 0.273. If these figures are accurate, why aren't these numbers (0.273) different from each other at this scale? Obviously, if measured to enough decimal places, differences will appear.

The Moon has less gravity and rotates at a different speed from the Earth. Why don't these cause variability in the different radius measurements? Do they cancel out? It is a coincidence? Is there something about the Earth-Moon dynamics that means over millions of years these proportions gradually equalise?


texts:
what does it mean 'The observations were made in the CO J=2–1 line and continuum at 230 GHz (1.3 mm)'?
"The observations of the continuum were also made with a bandwidth of 320 MHz. "
http://articles.adsabs.harvard.edu/pdf/2000A%26A...353L..25C

"Continuum at 230 GHz" seems like an example of oxymoron phrase?


texts: Why hasn't the CMB already receded away faster than the speed of light?

texts: If there are supposedly galaxies, or whole other parts of the universe, that we can't ever see due to them receding away from us faster than the speed of light, then why isn't or hasn't this occurred with the cosmic microwave background?


texts:
I am new to this domain and trying to understanding the fundamentals of local sidereal time.
Through an online available calculator https://www.iiap.res.in/personnel/reks/software/javascript/calclst.php ,I am noting down the local sidereal time for my longitude of interest. I have repeated the exercise for same time for five consecutive days. What I observe is that the local sidereal time is advancing by 0.06/07 hours per day for the same time.Like 21.88 Hours for current date and time , 21.94 Hours for the same time next day ,22.01 Hours for next to next day and the pattern continues. Kindly let me know how this increment is happening?


texts: Different approaches to quantify light pollution on a given location on Earth?

texts:
The question Light Pollution: what is the difference between artificial brightness and brightness and SQM made me wonder which different ways exist to directly and indirectly quantify light pollution at a given location on the Earth's surface? The obvious sources like Wikipedia etc. did not satisfiy my curiosity.
What I came up so far as a list of different methods is the following:

Look what you can observe with naked eye and use the Bortle scale.
Use a Sky quality meter of any kind and measure luminance.
Use the measurements of a pyranometer of your friendly metereologist or of an automatic weather station nearby and callibrate how many ${\rm W}/{\rm m}^2$ correspond to what value on the Bortle scale.
Use satellite data of any kind to obtain an approximate

If your urban area is bright enough, you could see that and in the visible spectrum of any weather satellite, and deduce a lower bound, i.e. how bright it must be at least on the ground.
The US's DOD might release maps from the Defense Metorological Satellite Program every now and then.

I am sure this list is not exhaustive - which other approaches am I missing?


texts: Is there a common metric to measure telescope power?

texts:
It is rather hard for me to compare telescopes due to the various numbers used.
600mm focal length and a 50mm diameter and eyepiece is a 12mm.
VS.
Focal length of 500 mm and the objective diameter is about 90 mm, Using a 3x Barlow Lens.
Is there something like an APR for telescopes?  Is there any objective rating system?  Most of the review videos just sound like sales pitches.
GC_


texts: How are the world's biggest telescopes cleaned?

texts:
How are the world's biggest telescopes, (such as the Very Large Telescope for example) cleaned?

My research includes what I have read about CO2 cleaning here. Are there any other ways to cleaning the mirrors? What if we were talking about the (cancelled) Overwhelmingly Large Telescope?


texts: Is there a flaw with the newer purposes and correlations attributed to the HR diagram? (And would a third axis of mass correct the enclosed flaw?)

texts:
When I was younger, I was looking at HR diagrams, and began to experiment with the HR diagram.

I was looking at plotting different groups of stars on the HR diagram when I found RV Tauri stars.

These are stars between 0.4 and 9 solar masses; they have reached the end of their "life" and the fusion shell of such a swollen star is advancing towards its surface (when it hits, the planetary nebula starts to form), thus its heats up and swells further. This phase occurs after the Asymptotic Giant Branch/Red Clump phases (AGB for high-metallicity stars, RC for low-metallicity stars).

Taking into account the above information, RV Tauri stars are BOTH more luminous and hotter at the surface than red giants (and AGB/RC stars), they should appear to the upper-left of the latter of the aforementioned groups (given the inversion of the temperature axis). All seemed well.

But then I saw this:

My knowledge of astrophysics tells me that due to stellar winds and the equation E=MC^2, a star's mass (after "birth") will usually decrease over time (unless receiving matter from another star). But if RV Tauri stars are above and to the left of red giants, it means that according to the graph, an increase in mass occurs every time a star migrates to the RV Tauri stage.

I know that all graphs have their limitations, but in my mind it was wrong to claim that these correlations were set in stone. Only axes could ever display data in a perfect way (they treat different units of data as separate simple measures, not "more unstable" compound measures). So I added a third axis of mass (as this is whole problem is to do with plotting the evolutionary "tracks" of stars); this is what is known to affect stellar evolution to the greatest extent. Here is what I came up with:

I did this in order to show that the HR diagram shows general trends of stars (not the evolutionary ones that scientists claim).

My question:

Was this a valid flaw with the HR diagram - and if so, is mass the best axis to add to it?

--EDIT--

The HR diagram is not flawed, I respect that. I also know that there will always be outliers. But the extra correlation of mass seems to be too flawed for that (as detailed above). My new question: is the attribution of these extra correlations wrong?


texts: I can't see any detail through my telescope

texts:
I have a AILINK 114mm diameter, 900mm focal length, reflector telescope. I'm able to see the moon very well however, I can't see Planets very clearly

The first two images are what I can see and the second two is what I want to see
Is that possible for my telescope also, how can I take better pictures like those examples.

Note* it was pre windy and the image was a little better then in the picture


texts: If oxygen were pumped into space where would it go?

texts: If an astronaut went into space with a sealed container of oxygen and opened it up in space and let all the oxygen go, what would happen to it? would it all just dissipate into some other particle or matter or would it just stay there until something consumed it